1. Technical Field
The present invention relates to a developing device and an image-forming apparatus.
2. Related Art
Among developing devices that use a two-component developer; that is, a developer containing a toner as a color material and a magnetic powder as a carrier, a so-called trickle-type developing device is known. A trickle-type developing device uses a technique of supplying two-component developer while discharging any excess two-component developer from a discharge port, to thereby prevent degradation of the two-component developer that could result from stirring of developer over an extended period of time.
Also known is a so-called rotary developing device, which comprises plural developer units that rotate as a unitary body to develop an electrostatic latent image formed on a surface of a photosensitive body. In such a rotary developing device, it is known to measure a mixture ratio of components of the accommodated two-component developer based on a change in magnetic permeability and to control the mixture ratio to maintain stability of image density.